1. Field of the Invention
The present invention is related generally to signs and visual warning devices which convey different information at different light intensity levels, and more particularly to a device which can be mounted on a motor vehicle and which conveys one or more messages when light of one or more predetermined intensities is incident upon the device.
2. Description of Related Art
When driving a motor vehicle, it is often necessary and/or advisable to send a signal to other drivers to warn them of the presence or anticipated movements of the first vehicle. Devices commonly used to convey such signals include head lights, tail lights, and turn signal indicators. These types of signals are all intended to warn the driver of the following vehicle of actions of the front vehicle. Another type of signal which can be sent by a driver is to simply flash his or her vehicle's headlights to warn the driver of a vehicle approaching from the front that his or her headlights are too bright and are distracting or temporarily blinding the first driver.
However, there are other common types of situations in which it has been virtually impossible to warn other drivers when they are doing something which is distracting and/or dangerous to someone else. For example, when driving at night, the driver of a front vehicle can also become distracted and/or temporarily blinded by headlights from a following vehicle when they are reflected in the rear view mirrors of the front vehicle. This often occurs when the following vehicle has approached the first vehicle too closely with its "high beam" on; when the headlights of the following vehicle are mounted high relative to the position of the driver in the first vehicle, such as when a truck approaches a passenger vehicle; or because the following vehicle's headlights are incorrectly adjusted. In any case, the situation is dangerous as well as annoying for the driver of the first vehicle because it interferes with his or her ability to see and react to road conditions.
A common solution to this problem is to use rear view mirrors which can be adjusted so that the intensity of the reflection is reduced. However, these adjustable mirrors have two major shortcomings. First, the intensity of all reflected light is reduced, thereby significantly decreasing the driver's ability to observe other objects and his or her depth perception of the reflected images. Such rear view mirrors are generally adjusted by a manually operated switch, so the driver is faced with a choice of (a) having to remove his or her hand from the steering wheel to adjust the mirror whenever bright lights approach from behind or (b) leaving the mirror adjusted for limited reflection and compromising his or her awareness of what is happening around his or her automobile. Second, such adjustable rear view mirrors are not generally mounted externally to the vehicle, and the driver can still be distracted or blinded by light reflected from externally mounted mirrors.
In principle, all vehicles could be required to have properly adjusted headlights and the use of headlight high beams could be prohibited, partially solving the problem of distraction and blinding by bright headlights of a following vehicle. However, it is impractical for all vehicles to have properly adjusted headlights at all times. Simply loading the trunk of a passenger vehicle for a short trip can significantly increase the angle between the ground and the vehicle's headlight beam, and it may not always be easy to readjust the headlights properly. Also, prohibiting the use of high beams in rural areas, where there is no ambient or overhead lighting along the roadway at night, would be dangerous, as it also would diminish the driver's ability to see bends and obstacles in the road. Further, these requirements would not eliminate the situation where the driver of the first vehicle is exposed to intense light coming from a following truck or other vehicle with headlights mounted relatively high.
All of the signaling methods discussed above require the use of equipment which is placed in essentially all road vehicles during the manufacturing process. Headlights, tail lights, turn signals, and rear view mirrors are all relatively expensive items. Also, many of the existing signaling devices, including some rear view mirrors, utilize light sources and, therefore, installation requires the emplacement of wiring and connection to the vehicle's electrical system.
Thus, there is a need for a device which conveys different information with different incident light intensities. There is a further need for a device which provides a signal to a following driver that his or her vehicle's headlights are dangerously bright when reflected into the eyes of the driver of the forward vehicle. Preferably, such a signal can be transmitted without sending such a signal to other nearby drivers whose headlights are not offensive. There is a still further need for a signaling device with a signal which is visible only when the reflection is sufficiently bright to distract the driver of the forward vehicle. There is yet a further need for such a warning device which is inexpensive to produce. There is an additional need for a warning device which can be easily and inexpensively mounted to a vehicle at some time after the vehicle is manufactured. There is also a need for a device which operates by passive illumination, without requiring a light source powered by the electrical system of the vehicle to which it is mounted.